The invention relates to a method for damping vibration on a vehicle wheel suspension with a hydraulic vibration damper.
German patent document DE 37 29 187 C2 describes a vibration damper with which the damping forces are adjustable for both directions of movement, indefinitely and independently, even during a spring deflection and recoil movement. Such a vibration damper has at least two working chambers separated by a piston with main overflow valves. A piston rod attached to the piston is guided through one of the working chambers. In addition to the main overflow valves, the working chambers are connected by an overflow opening that has an adjustable opening cross section. A control element held in a resting position in which the overflow opening is at its maximum size is triggered such that the size of the overflow opening is reduced as needed and thus the damping effect induced by the vibration damper is increased. The control element may be operated electrically, magnetically, hydraulically or by inertial forces, for example. DE 199 21 125 A1 discloses an inertial force-controlled device for adjusting the opening cross section of an overflow channel between the working chambers.
The disclosure content of German patent documents DE 37 29 187 C2 and DE 199 21 125 A1 is herewith included explicitly in the present description to ensure a complete disclosure of all the functions of the vibration damper.
In adjusting the damping force of a motor vehicle, the damping force characteristic up to approximately 1-2 m/s piston speed is considered with regard to comfort and driving safety. As a rule, a slightly progressive rise is obtained automatically from the selected piston/valve combination for damper characteristics greater than 2 m/s. However, this is not usually taken into account separately in chassis design.
At very high vertical wheel speeds much greater than 2 m/s, such as those occurring when driving over a pothole or a threshold, for example, great loads occur in the vehicle body and chassis in the end stop range due to accelerated unsprung masses. In the usual vibration dampers, the damping force for such high piston speeds is too low to adequately dissipate the kinetic energy of the accelerated wheel, which means that most of the energy must be carried by the body structure. This means that the structural components involved are massive and heavy and are therefore expensive to manufacture. If the damping force of the vibration damper is increased on the whole, this has a negative effect on driving comfort at a vertical speed of less than 2 m/s.
Therefore, the object of the present invention is to provide a vibration damping method on a motor vehicle wheel suspension by means of a hydraulic vibration damper which prevents great loads on the vehicle body and chassis caused by very large vertical velocities of the wheel, e.g., when traveling over potholes or thresholds, and to do so without making any sacrifice in driving comfort or driving safety.
In a hydraulic vibration damper for a motor vehicle, a method of vibration damping on a wheel suspension used according to the present invention is characterized in that the damping force of the vibration damper increases as a function of piston speed, especially in the piston speed range of essentially 0 to 2 m/s, at first increasing slowly, essentially linearly, and then, especially above a piston speed of essentially 2 m/s, increasing according to a highly progressive function.
This has the advantage that the vibration damper prevents great loads on the body and chassis caused by very high vertical wheel speeds, e.g., when driving over an obstacle or a threshold, and does so without any sacrifice in terms of driving comfort or driving safety. Due to the highly progressive rise in damping force, especially beyond a piston speed of essentially 2 m/s, the vibration damper dissipates the energy of high vertical wheel speeds more rapidly and therefore prevents great loads on the body and chassis. The piston speed, beyond which a highly progressive rise in the damping force is to advantageously take place, is defined by the end of the comfort-relevant range in chassis design. According to the present consensus, the comfort-relevant range for passenger vehicles ends at a piston speed of approximately 2 m/s. However, this value may easily be 1 m/s to 4 m/s for certain desired vehicle properties due to differences in chassis design.
Through a suitable choice, design and construction of vibration damper valves or by otherwise influencing the hydraulic resistances in the vibration damper, it is possible to implement a characteristic which is generated by damping forces known from the state of the art in the piston speed range up to the end of the range that is relevant for comfort. Beyond this piston speed range, an extreme progression in the damper characteristic is induced to decelerate the accelerated masses to a greater extent. This ultimately produces reduced loads in the vehicle body and chassis owing to a lower residual energy in the end stop area and also permits lighter and less expensive designs of the vehicle body, chassis and the vehicle itself. This is especially advantageous for vehicles having a low range of the spring, e.g., for sporty vehicles with a low design. A longer vehicle lifetime under poor road conditions is achieved with less damage to the body structure.
In a preferred embodiment of the vibration damping method, the characteristic of the damping force runs essentially as a function of the piston speed, following the highly progressive rise, continuing with a steeper, essentially linear rise.
It is even more advantageous if, following the steep, essentially linear course or following the highly progressive rise in the characteristic curve of the damping force as a function of piston speed, this characteristic curve then develops into an essentially linear course with a slight increase.
In other preferred embodiments of the vibration damping method, the vibration damper has an adjustment device for the damping force it produces. By operation of this adjustment device, the characteristic of the damping force may be displaced essentially along the abscissa as a function of the piston speed.
The starting point of the progression, which is defined by the design, is therefore advantageously adjustable.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings for example.